How Many Types of Bacteria Are Found in the Mouth?

Human saliva is thought to contain more than 700 species of bacteria — more than 21 species per square inch (6.5 sq cm) of mouth space. People tend to have individual blends of mouth bacteria, too. The type of bacteria in a person's mouth can be affected by disease, diet and possible even his or her weight, because people who are overweight have different types of bacteria in their mouths than people who are within a normal weight range.

More facts about saliva and bacteria:

Humans in general have thousands of species of bacteria living in and on the body, and there are at least 10 times the number of bacteria cells living in and on the body than there are human cells.

Besides hosting bacteria, saliva also protects teeth by keeping the mouth slightly alkaline, and it has a lot of antimicrobial substances and antibodies. This mix is so powerful that it can sometimes even disable the human immunodeficiency virus (HIV).

Advances in medicine might eventually lead to scientists being able to diagnose illnesses, including cancer and heart problems, from a simple spit test.